Circuit breaker with an improved actuating mechanism

ABSTRACT

A circuit breaker having an automatically resettable linkage mechanism which includes a pivotal link for moving the circuit breaker contacts between the open and closed positions. The circuit breaker also includes a manual actuating mechanism which engages the pivotal link and is operable to manually move the contacts to the &#39;&#39;&#39;&#39;closed&#39;&#39;&#39;&#39; position but is inoperable to subsequently manually move the contacts to the &#39;&#39;&#39;&#39;open&#39;&#39;&#39;&#39; position and which is itself reset by the reset movement of the pivotal link after the collapse of the linkage mechanism in response to the occurrence of a preselected electrical condition.

I United States Patent [151 3,680,014 Wilkinson July 25, 1972 [54] CIRCUIT BREAKER WITH AN 2,952,757 9/1960 Ellenberger ..337/66 IMPROVED ACTUATING MECHANISM 3,075,058 1/1963 Platz et a1. ..335/26 [72] Inventor: John C. Wilkinson, Lawrenceville, NJ. Primary Examiner Hamld Broome [73] Assignee: lleinemann Electric Company, Trenton, Attorney-Denny & Denny 22 Filed: Jan. 19, 1971 [57] ABSTRACT A circuit breaker having an automatically resettable linkage [2!] Appl' l076l8 mechanism which includes a pivotal link for moving the circuit breaker contacts between the open and closed positions. [52] US. Cl ..335/26, 335/25 The circuit breaker also includes a manual actuating a 0 77/02 mechanism which engages the pivotal link and is o erable to P [58] Fleld of Search ..335/26, 27, 28, 25, 24; manually move the contacts to the position but is 337/66 74 operable to subsequently manually move the contacts to the open" position and which is itself reset by the reset move- [56] References C'ted ment of the pivotal link after the collapse of the linkage UNITED STATES PATENTS mechanism in response to the occurrence of a preselected electrical condition. 3,193,644 7/1965 Coughlin et a1 ..335/27 3,257,523 6/1966 Clarke ..335/26 15 Claims, 3 Drawing Figures CIRCUIT BREAKER WITH AN IMPROVED ACTUATING MECHANISM BACKGROUND OF THE INVENTION This invention relates to circuit breakers and the like and, more particularly, to a new and improved actuating mechanism therefor.

Among the several objects of the invention is the provision of an actuating mechanism for converting a circuit breaker operated by a pivotal handle link to one which is operable by a rocker handle.

A further object of the invention is the provision of a circuit breaker which can be turned on" manually, turned off automatically upon the occurrence of a predetermined condition, but which cannot be turned off manually.

A further object is the provision of an actuating mechanism of the rocker handle type operable to manually turn on" a circuit breaker, inoperable to turn if ofF manually while the circuit breaker is in the on condition, and resettable automatically in response to the collapsing movement of the circuit breaker mechanism to render it operable again to manually turn on the circuit breaker.

Still another object is the conversion of a known circuit breaker operable by means of a pivotal handle to a rocker handle actuated circuit breaker having the above noted properties with a minimum change in the construction and operation of the circuit breaker mechanism itself.

BRIEF DESCRIPTION OF THE VIEWS In the drawings:

FIG. 1 shows the circuit breaker assembly of the invention in side elevation with one of the half-cases partially broken away to expose the operating mechanism in the contacts open" and fully reset, and with the actuating mechanism mounted to the case of the circuit breaker and shown partly in cross section, the rocker handle of the actuating mechanism being in the off or reset" position;

FIG. 2 is a view similar to FIG. 1 but showing the operating mechanism of the circuit breaker in the contacts closed" position and the rocker handle in the on position; and

FIG 3 is a sectional view of the rocker handle actuating mechanism taken along the line 3-3 in FIG. 1.

DETAILED DESCRIPTION Referring to FIGS. 1 and 2, the invention is generally comprised of two subassemblies, a circuit breaker l0, and a manual actuating mechanism 12 attached to the circuit breaker case 40.

The circuit breaker I is generally similar to that described in US. Pat. No. 3,329,913 except that the handle for manually operating the circuit breaker mechanism has been eliminated and the upper contour of the pivotal link has been altered, as described in detail below. In view of the similarity between the circuit breaker in the above noted patent and the one employed in this invention, only a brief description of the operating mechanism of the circuit breaker will be given immediately hereinafter.

The mechanism 41 comprises a movable contact 42 carried by a movable arm 43 and engageable with a stationary contact 44, the latter carried by terminal 45. The movable arm 43 is connected by a flexible conductor 47 to one end of a coil 48 forming part of an electromagnetic device 50. The electromagnetic device 50, on predetermined electrical conditions, causes the collapse of the linkage mechanism I to trip open the contacts 42 and 44 on the occurrence of the predetermined conditions. The electrical circuit of the circuit breaker is completed by connecting the other end of the coil 48 to the terminal 46.

Further, the movable arm 43 is biased by a spring 52 toward the open position of the contacts 42 and 44 and is mounted on a pin 53 about which it pivots, the pin 53 being carried by two spaced plates 54 which are integral with an L-shaped member 56 and jointly form a frame 59 for carrying the coil 48. The

end portions of the pin 53 extend into holes formed in the opposed side walls of the half-cases 37 to properly locate and support the mechanism 41 inside the casing 40. Another pin 62, carried by the movable arm 43, has end portions which engage the spaced plates 54 to limit the opening movement of the arm 43, as shown in FIG. 1.

The movable arm 43 is also connected by a pin 57 to a toggle assembly or latching mechanism 58, the latter being in turn connected to an arm 65 of the pivotal lever or link 60 by a pin 61. The link 60 pivots about a pin 64 having its end portions also carried by the spaced plates 54. A spring 55 is coiled on the pin 64 and has one end attached to one of the frame plates 54 and the other end of the spring 55 is in contact with the pin 61, the spring being stressed at all times so as to bias the link 60 to the contacts open" position, FIG. 1. After tripping of the toggle assembly 58 in response to an overload, for instance, the link spring 55 automatically moves the link 60 from the contacts closed position, FIG. 2, to the contacts open position, FIG. I.

The pivotal link 60 has an approximately semi-circular recess formed in its upper portion, the recess 80 being bounded by upwardly projecting legs 81. An operating rod 84 is carried in slots in the legs 81 and spans the recess 80 near the apex of the link 60. The pivotal link 60 will normally be held in one or the other of two stable positions, the contacts open" position, FIG. 1, or the contacts closed" position, FIG. 2. The pivotal link 60 is moved between these two positions by the actuating mechanism 12 which is mounted thereabove and engages the operating rod 84 as will be explained in more detail hereinafter.

The frame 59 forms a part of the electromagnetic device 50 to which is secured a time delay tube 63 housing a spring biased magnetizable core (not shown) movable against the re tarding action of a suitable fluid to provide a time delay before tripping of the mechanism on certain overloads.

The operation of the type of linkage mechanism 51 and electromagnetic device 50 is specifically set forth in US Pat. No. 3,329,913 and for purposes of brevity it will only be generally described herein as follows -when the pivotal link 60 is moved from the contacts open position, i.e., the off position, FIG. I, to the contacts closed" position, FIG. 2, the toggle assembly 58 and the movable arm 43 all move down, against the bias of the spring 52, and move the contacts 42 into engagement with the stationary contact 44 achieving the contacts closed" position, i.e., the "on" position as illustrated in FIG. 2.

Upon occurrence of a predetermined overload condition, assuming the circuit breaker to be in the contacts "closed" position, the armature 70, which is also part of the electromagnetic device 50, is attracted toward the pole piece 72, either after a time delay period or virtually instantaneously, depending on the overload condition. The armature 70 is pivoted on a pin 74 whose end portions are also carried by suitable holes in the frame plates 54. The armature 70 also includes an attractable part 73 and a trip finger 71, and when the attracted part 73 of the armature 70 pivots toward the pole piece 72, the trip finger 71 pivots to the right as seen in FIG. 2 and engages and trips the arm 75 forming part of the linkage mechanism 51, which is opposite the trip finger 71 when the toggle assembly 58 is in the contact closed position, FIG. 2, whereupon the toggle assembly 58 collapses and the movable arm 43 moves upward under the bias of spring 52 to open the contacts 42 and 44. The toggle assembly 58 is automatically relatched and simultaneously the pivotal link 60 is also moved to the contacts open position, FIG. 1, under the pressure applied by the spring 55. Thus, the pivotal link 60 is returned from the position shown in FIG. 2 to the position shown in FIG. 1.

As is well-known, a plurality of U-shaped magnetizable grids 66 are placed adjacent the movable and stationary contacts 42 and 44 to minimize any arc that may form between the contacts upon opening.

The case 40 of the circuit breaker also includes an opening 25 into which the upper portion of the handle link 60 projects. The opening 25 is bounded by an approximately circular boss 26 formed integral with the circuit breaker case 40.

The actuator mechanism 12 comprises a rocker handle 85 and a mounting bracket 86 for attaching the rocker handle 85 to the circuit breaker case 40 in a position to properly operate the handle link 60 of the circuit breaker mechanism 41. The mounting bracket 86 for the actuator mechanism 12 consists of a main body portion 87 which, when the actuator unit is mounted on the case 40, lies generally parallel to and abutting the upper surface of the circuit breaker case 40. The main body portion 87 of the bracket 86 includes two pairs of arms 88 which project in a direction away from the rocker handle 85, one pair of arms located at each end of the main body portion 87. Each of the pairs of arms 88 interfits into a corner recess 89 in the case 40 of the circuit breaker 10 to thereby straddle the upper surface of the case 40. The arms 88 contain openings which are aligned with openings in the corners of the circuit breaker case 40. Rivets 90 are passed through the aligned openings in the arms 88 and corners of the case 40 to hold the actuator mechanism 12 in abutment with the upper surface of the case.

The main body portion 87 of themounting bracket 86 may include two flanges 91, the upper portions of which extend approximately parallel to the upper surface of the case 40 and in a direction away from the rocker handle 85. These flanges may contain threaded holes 92 which may be used for mounting the circuit breaker 10 to a panel (notshown) with the rocker handle 85 projecting through a hole in the panel. The main body portion 87 further contains a circular opening which registers with the boss 26 on the upper surface of the circuit breaker case 40.

The main body portion 87 of the bracket 86 also includes two spaced apart, inverted V-shaped ears 104 integral with and projecting upwardly from opposite sides of the bracket 86. The apexes of the ears 104 include holes which jointly carry a mounting pin 106 on which the rocker handle 85 is pivotally supported.

The rocker handle 85 may be made of a plastic material and comprises two upper flat surfaces 108 and 109 intersecting each other to form a shallow V. The flat surfaces 108 and 109 may be used to indicate the condition of the circuit breaker by having imprinted thereon the words on (on surface 108) or off (on surface 109). Depending on the condition of the circuit breaker, one of these indications is oriented approximately parallel or flush with the adjacent surfaces of a panel (not shown) to which the circuit breaker I0 is mounted while the other indication projects upward above the panel and at an angle thereto.

The rocker handle 85 also includes a centrally disposed arm 110 which projects into the opening 26 in the top margin of the circuit breaker case 40 to a position immediately overlying the handle link 60. The arm 110 has a centrally located opening through which the mounting pin 106 passes to pivotally support the rocker handle 85 and may be thickened somewhat in the area of this opening for greater strength and stability.

The lower portion of the arm 110 adjacent the operating rod 84 of the handle link 60 includes a first wall segment 112 which extends beyond the operating rod 84 on one side thereof. The pivotal path of movement of the first wall segment 112 in moving between the on and ofF positions of the rocker handle 85 cuts across and is traverse to the path of movement of the operating rod 84 in moving between the contacts open" and contacts closed" positions of the handle link 60.- It is thus seen that upon manual movement of the rocker handle 85 from its off position, FIG. 1, to its on" position, FIG. 2, the wall segment 112 abuts the operating rod 84 and thereby moves the pivotal link 60 from the contacts open" position, FIG. 1, to contacts closed" position, FIG. 2.

A torsion spring 113 is wrapped about the mounting pin 106 in a position intermediate the arm 110 and one of the ears 104. One end of the spring 113 is attached to one of the ears 104, the other end bearing against the underside of the upper flat surface 109 carrying the off indication. The spring 113, therefore, continuously biases the rocker handle towards its on" position and continuously biases the first wall segment 112 into abutment with the operating rod 84 on the handle link 60, but is weaker than the reset spring 55 which biases the handle link 60 to its contacts "open" position.

The lower portion of the arm further includes a second wall segment 115 which defines partially a void or recess 116 on the side of the operating rod 84 opposite the first wall segment 112. The shape of the recess may vary so long as it extends across the path of motion of the operating rod 84 of the handle link 60 in moving between the contacts open and contacts closed" positions. Thus, it is seen that, with the handle link 60 in the contacts closed" position, FIG. 2, the recess 116 prevents the opening of the circuit breaker contacts through manual movement of the rocker handle 85 by preventing abutment between the rocker handle 85 and the side of the operating rod 84 opposite the wall segment 112.

In operation, with the circuit breaker 10 in the position shown in FIG. 1, when the projecting upper surface 108 of the rocker handle 85 is manually depressed, the arm 110 pivots in a counterclockwise direction and the first wall segment 112 bears against the operating rod 84 in the upper portion of the handle link 60. This counterclockwise movement pivots the handle link 60 about the pin 64 and moves the operating mechanism 41 of the circuit breaker l0 and the contacts 42 and 44 to their contact closed" positions, as shown in FIG. 2.

With the handle link 60, the operating mechanism 41 and contacts 42 and 44 in their closed positions, the rocker handle 85 is held in its on position by means of the bias applied by the spring 113 to the underside of the flat surface 109. With the elements in the position shown in FIG. 2, it is not possible to manually open the contacts 42 and 44 of the circuit breaker 10 by means of manual rotation of the rocker handle 85. This results from the location of the recess 116 to the right of the operating rod 84 of the handle link 60 as seen in FIG. 2.

Upon the occurrence of the preselected electrical condition the trip finger 71 of the armature 70 releases the latch assembly 58 and allows the linkage mechanism 51 to collapse. The collapse of the linkage mechanism 51 permits the handle link reset spring 55 to move the handle link 60 and the operating rod 84 in, the counterclockwise direction. During this counterclockwise movement of the handle link 60 the operating rod 84 abuts the first wall segment 112 and automatically pushes it and the rocker handle 85 from the on to the ofi or reset position.

It would be equally possible to arrange the spring 113 to continuously bias the rocker handle 85 toward its ofP' position by having one of its ends attached to one of the ears 104 while the other end is positioned to exert an upward force on the upper surface 108 of the rocker handle. With the above arrangement, after the movement of the operating mechanism 41 to the contacts closed position, the rocker handle 85 would immediately return to the off position upon the withdrawal of manual pressure. Resetting of the rocker handle 85 by the operating mechanism 41 of the circuit breaker 10 would not be required in this arrangement.

Having described this invention, what I claim is:

1. In combination, a circuit breaker including a case, a pair of contacts enclosed by the case, an automatically resettable collapsible operating mechanism to move one of the contacts between closed and open" positions, said mechanism including a pivotal link to operate said mechanism, tripping means engageable with said operating mechanism for collapsing said mechanism upon the occurrence of a preselected electrical condition to move said contacts from the closed" to the open" position, and an actuating mechanism movable between an on" position and an off position and engageable with said pivotal link during movement of said actuating mechanism from the off to the on position for moving said operating mechanism from the contacts open" to the contacts closed position, but not engageable with said pivotal link during movement of said actuating mechanism from the on to the off position.

2. The combination recited in claim 1 wherein said actuating mechanism is a separate unit attachable to the exterior of said case.

3. The combination recited in claim 2 wherein said actuating mechanism includes a mounting bracket attachable to said case, said case contains an opening overlying said pivotal link, and said actuating mechanism includes an actuating arm supported by said bracket and projecting through said opening to engage said pivotal link.

4. The combination recited in claim 1 wherein said actuating mechanism is reset from the on" position to the of! position in response to the collapsing movement of said operating mechanism upon the occurrence of said preselected condition.

5. The combination recited in claim 1 wherein said pivotal link includes an operating rod for moving said link between the contacts open and contacts closed positions, said actuating mechanism comprises a first wall segment extending to one side of said rod to move said link to the contacts closed position, and said means for preventing manual movement of said contacts to the open" position comprises a recess located on the other side of said rod and extending traverse to the path of movement of said rod in moving from the contacts open to the contacts closed positions.

6. In combination, a case, a pair of contacts housed in said case and movable relative to each other between a contacts open and a contacts closed position, an automatically resettable collapsible operating mechanism for effecting the relative movement of said contacts, tripping means for collapsing said operating mechanism to move said contacts from the contacts closed to the contacts open position upon the occurrence of a preselected electrical condition, and a unitary actuating mechanism attachable to said case compris ing a first wall segment engageable with said operating mechanism for moving said operating mechanism in response to an external command to effect the closing of said contacts, said actuating mechanism further including a recess for preventing subsequent engagement of said operating mechanism by said actuating mechanism to prevent movement of said contacts from the contacts closed position to the contacts open position in response to an external command.

7. The combination recited in claim 6 wherein said operating mechanism includes a pivotal link, said case contains an opening adjacent said pivotal link, said actuating mechanism includes a mounting bracket having an opening in registry with said opening in said case, and a rocker handle pivotally supported from said bracket, said rocker handle including an arm extending through said openings in said bracket and case to a position adjacent said pivotal link, said first wall segment and said recess being formed in said arm.

8. The combination recited in claim 7 wherein said arm is pivotally carried by said bracket, said pivotal link includes an operating rod mounted therein adjacent said arm, said wall segment extending to one side of said rod and traverse to the path of movement of said rod and said recess in said arm located to the side of said rod opposite said wall segment and extending traverse to the path of movement thereof.

9. The combination recited in claim 8 wherein said rocker handle is movable between on" and of? positions, cormitting said actuating mechanism responding to said contacts closed" and "open" positions, respectively, and further including a spring for continuously biasing said rocker handle toward the "on" position.

10. The combination recited in claim 9 wherein said rocker handle is automatically reset to the of? position in response to the collapsing movement of said operating mechanism.

11. A circuit breaker comprising a housing, a pair of contacts located within said housing, a collapsible automatically resettable operating mechanism movable between contacts open" and contacts closed" positions for effecting the relative movementof said contacts between contacts open" and closed" positions, respectively, tripping means to collapse said mechanism when it is in the contacts "closed" position in response to a preselected condition to open said contacts, and means associated with said operating mechanism and operable between on and off positions to manually move said operating mechanism from said contacts open" position to said contacts closed position during movement from the off to the on position and freely movable from the on" position to the off position when the operating mechanism is in the contacts closed position.

12. A circuit breaker comprising a housing, a pair of contacts located within said housing, a collapsible linkage coupled to one of said contacts and movable between open" and closed" positions for affecting the relative movement of said contacts between contacts open and contacts closed" positions, respectively, tripping means for collapsing said linkage in response to a preselected electrical condition to open said contacts, and an actuating mechanism movable between on" and off positions including means for engaging said linkage during movement from said off" position to said on position to move said contacts from the contacts open" position to the contacts closed" position and means for perto move out of engagement with said linkage from said on" position to said 01? position when said linkage is in the contacts closed position without opening said contacts.

13. The combination recited in claim 12 wherein said actuating mechanism comprises a subassembly and means for attaching said subassembly to said housing.

14. The combination recited in claim 13 further including a pivotal link coupled to said linkage and an opening in said case overlying said pivotal link, and wherein said means for engaging said linkage comprises an arm extending through said opening to a position adjacent said pivotal link and said means for permitting said actuating mechanism to move out of contact with said linkage comprises a recess in said arm.

15. The combination recited in claim 13 further including a pivotal link coupled to said linkage and an opening in said case overlying said pivotal link, said pivotal link movable between an open" and a closed" position corresponding to said contacts open and contacts closed positions, respectively, said pivotal link including an operating rod for moving said link between the contacts open and contacts closed positions, said means for engaging said linkage comprising an arm extending to one side of said rod and movable into abutment therewith to move said link to the closed position, and said means for permitting said actuating mechanism to move out of abutment with said linkage comprising a recess in said arm located on the other side of said rod and extending traverse to the path of movement of said rod in moving from the open" to the closed" position. 

1. In combination, a circuit breaker including a case, a pair of contacts enclosed by the case, an automatically resettable collapsible operating mechanism to move one of the contacts between ''''closed'''' and ''''open'''' positions, said mechanism including a pivotal link to operate said mechanism, tripping means engageable with said operating mechanism for collapsing said mechanism upon the occurrence of a preselected electrical condition to move said contacts from the ''''closed'''' to the ''''open'''' position, and an actuating mechanism movable between an ''''on'''' position and an ''''off'''' position and engageable with said pivotal link during movement of said actuating mechanism from the ''''off'''' to the ''''on'''' position for moving said operating mechanism from the contacts ''''open'''' to the contacts ''''closed'''' position, but not engageable with said pivotal link during movement of said actuating mechanism from the ''''on'''' to the ''''off'''' position.
 2. The combination recited in claim 1 wherein said actuating mechanism is a separate unit attachable to the exterior of said case.
 3. The combination recited in claim 2 wherein said actuating mechanism includes a mounting bracket attachable to said case, said case contains an opening overlying said pivotal link, and said actuating mechanism includes an actuating arm supported by said bracket and projecting through said opening to engage said pivotal link.
 4. The combination recited in claim 1 wherein said actuating mechanism is reset from the ''''on'''' position to the ''''off'''' position in response to the collapsing movement of said operating mechanism upon the occurrence of said preselected condition.
 5. The combination recited in claim 1 wherein said pivotal link includes an operating rod for moving said link between the contacts ''''open'''' and contacts ''''closed'''' positions, said actuating mechanism comprises a first wall segment extending to one side of said rod to move said link to the contacts ''''closed'''' position, and said means for preventing manual movement of said contacts to the ''''open'''' position comprises a recess located on the other side of said rod and extending traverse to the path of movement of said rod in moving from the contacts ''''open'''' to the contacts ''''closed'''' positions.
 6. In combination, a case, a pair of contacts housed in said case and movable relative to each other between a contacts ''''open'''' and a contacts ''''closed'''' position, an automatically resettable collapsible operating mechanism for effecting the relative movement of said contacts, tripping means for collapsing said operating mechanism to move said contacts from the contacts ''''closed'''' to the contacts ''''open'''' position upon the occurrence of a preselected electrical condition, and a unitary actuating mecHanism attachable to said case comprising a first wall segment engageable with said operating mechanism for moving said operating mechanism in response to an external command to effect the closing of said contacts, said actuating mechanism further including a recess for preventing subsequent engagement of said operating mechanism by said actuating mechanism to prevent movement of said contacts from the contacts ''''closed'''' position to the contacts ''''open'''' position in response to an external command.
 7. The combination recited in claim 6 wherein said operating mechanism includes a pivotal link, said case contains an opening adjacent said pivotal link, said actuating mechanism includes a mounting bracket having an opening in registry with said opening in said case, and a rocker handle pivotally supported from said bracket, said rocker handle including an arm extending through said openings in said bracket and case to a position adjacent said pivotal link, said first wall segment and said recess being formed in said arm.
 8. The combination recited in claim 7 wherein said arm is pivotally carried by said bracket, said pivotal link includes an operating rod mounted therein adjacent said arm, said wall segment extending to one side of said rod and traverse to the path of movement of said rod and said recess in said arm located to the side of said rod opposite said wall segment and extending traverse to the path of movement thereof.
 9. The combination recited in claim 8 wherein said rocker handle is movable between ''''on'''' and ''''off'''' positions, corresponding to said contacts ''''closed'''' and ''''open'''' positions, respectively, and further including a spring for continuously biasing said rocker handle toward the ''''on'''' position.
 10. The combination recited in claim 9 wherein said rocker handle is automatically reset to the ''''off'''' position in response to the collapsing movement of said operating mechanism.
 11. A circuit breaker comprising a housing, a pair of contacts located within said housing, a collapsible automatically resettable operating mechanism movable between contacts ''''open'''' and contacts ''''closed'''' positions for effecting the relative movement of said contacts between contacts ''''open'''' and ''''closed'''' positions, respectively, tripping means to collapse said mechanism when it is in the contacts ''''closed'''' position in response to a preselected condition to open said contacts, and means associated with said operating mechanism and operable between ''''on'''' and ''''off'''' positions to manually move said operating mechanism from said contacts ''''open'''' position to said contacts ''''closed'''' position during movement from the ''''off'''' to the ''''on'''' position and freely movable from the ''''on'''' position to the ''''off'''' position when the operating mechanism is in the contacts ''''closed'''' position.
 12. A circuit breaker comprising a housing, a pair of contacts located within said housing, a collapsible linkage coupled to one of said contacts and movable between ''''open'''' and ''''closed'''' positions for affecting the relative movement of said contacts between contacts ''''open'''' and contacts ''''closed'''' positions, respectively, tripping means for collapsing said linkage in response to a preselected electrical condition to open said contacts, and an actuating mechanism movable between ''''on'''' and ''''off'''' positions including means for engaging said linkage during movement from said ''''off'''' position to said ''''on'''' position to move said contacts from the contacts ''''open'''' position to the contacts ''''closed'''' position and means for permitting said actuating mechanism to move out of engagement with said linkage from said ''''on'''' position to said ''''off'''' position when said linkage is in the contacts closed position without opening said contacts.
 13. The combination recited in claim 12 wherein said actuating mechanism comprises a subassembly and means for attaching said subassembly to said housing.
 14. The combination recited in claim 13 further including a pivotal link coupled to said linkage and an opening in said case overlying said pivotal link, and wherein said means for engaging said linkage comprises an arm extending through said opening to a position adjacent said pivotal link and said means for permitting said actuating mechanism to move out of contact with said linkage comprises a recess in said arm.
 15. The combination recited in claim 13 further including a pivotal link coupled to said linkage and an opening in said case overlying said pivotal link, said pivotal link movable between an ''''open'''' and a ''''closed'''' position corresponding to said contacts ''''open'''' and contacts ''''closed'''' positions, respectively, said pivotal link including an operating rod for moving said link between the contacts ''''open'''' and contacts ''''closed'''' positions, said means for engaging said linkage comprising an arm extending to one side of said rod and movable into abutment therewith to move said link to the ''''closed'''' position, and said means for permitting said actuating mechanism to move out of abutment with said linkage comprising a recess in said arm located on the other side of said rod and extending traverse to the path of movement of said rod in moving from the ''''open'''' to the ''''closed'''' position. 